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High pathology avian flu detected in mammals

2 February 2023

Bird flu (Avian Influenza A, H5N1) has recently been detected in mammals including otters, foxes and seals (in the UK and on the continent), which raises concerns both for mammal populations, and for human health. Defra have recently published an update on risks to human health, which incorporates some information on infection in mammals.


It is probable that infections identified in UK mammals so far have arisen via scavenging (mammals eating wild birds which had died from avian flu). However - the virus evidently survives well in water too - transmission between birds is often via faeces in water, which is likely to increase risk to aquatic/semi-aquatic mammals. There is therefore risk from:

  • Contact with water contaminated with faeces from infected animals.
  • Contact with bodily fluids/faeces from infected animals.
  • Consumption of infected carcasses.
  • Inhalation of virus (i.e. being in close contact with a live infected animal).


Prevalence in mammals is currently unknown. Although 9 cases have been detected so far in the UK (4 otters and 5 foxes; confirmed findings from the Animal Health and Plant Agency), these have all originated from testing of individuals that died in areas of known bird flu outbreaks, where they had presumably been scavenging on dead wildfowl. There is no published data describing prevalence in randomly sampled mammals from the wider wild populations.

At CUOP we have now established a screening system, and are sending swab samples from all otters we receive from across England/Wales/Scotland (largely as a result of roadkill) for testing, which will enable us to evaluate prevalence within the wild population.

So far (as at 02/02/2023) we have received results from 48 otters (from across England/Wales) all of which have tested negative (i.e. no evidence of bird flu infection so far).


There is evidence of disease (particularly meningoencephalitis) and mortality in infected mammals, including seals, otters and foxes (for example Encephalitis and Death in Wild Mammals at a Rehabilitation Center after Infection with Highly Pathogenic Avian Influenza A(H5N8) Virus, United Kingdom). For H5N8, that study demonstrated that viral genomes isolated from infected mammalian cells showed a mutational change that is associated with increased virulence and replication in mammals. However, there is currently insufficient data on infected mammals (including humans) to evaluate population-level risk in depth.

Impact on our post mortem programme

Because of the potential exposure risk to our team during prolonged contact with carcasses during post mortem (PM), we have been advised not to carry out PMs on otters until we have negative screening results. We are therefore taking swabs (rectal, nasal and tracheal) in a controlled cabinet, and then refreezing the bodies, while we wait for swab results.

Currently we do not have facilities suitable for handling otters testing positive for HPAI, and any otters testing positive will have to be incinerated without PM (we are exploring other options on this). We will proceed with full PM only on otters that test negative.

Precautions to minimise risk to humans

Animals found dead should not be handled unnecessarily, or without taking appropriate precautions. Anyone from our collection network who is picking up otter carcasses should take precautions as advised for handling potentially infected birds.

Key points to be aware of are:

  • There is a risk of mammal/bird to human transmission if you are in contact with infected animals
  • Flu vaccination is likely to give some (but not full) protection and is advisable for anyone likely to be handling potentially infected mammals
  • PPE should be worn when handling potentially infected mammals, including gloves and masks
  • Hygiene precautions should be taken including washing down/disinfecting any potentially contaminated surfaces
  • Anti-viral medication can be prescribed by the GP if there is an identified infection risk: anyone exposed to an infected animal should urgently consult their GP
  • Testing specific to avian flu can be carried out: anyone developing flu-like symptoms after being in contact with a potentially infected animal (e.g. after handling an otter carcass) should inform their GP.